An isolation tank is a lightless, soundproof tank inside which subjects float in salt water at skin temperature. They were first used by John C. Lilly[1] in 1954 to test the effects of sensory deprivation. Such tanks are now also used for meditation and relaxation and in alternative medicine. The isolation tank was originally called the sensory deprivation tank. Other names for the isolation tank include flotation tank, float tank, John C. Lilly tank, REST tank, and sensory attenuation tank.

The flotation tank was developed in 1954 by John C. Lilly, a medical practitioner and neuro-psychiatrist.[2][3][4] During his training in psychoanalysis at the US National Institute of Mental Health (NIMH), Lilly commenced experiments with sensory deprivation in combination with a psychedelic agent, mostly LSD. In neurophysiology, there had been an open question as to what keeps the brain going and the origin of its energy sources. One hypothesis was that the energy sources are biological and internal and do not depend upon the outside environment. It was argued that if all stimuli are cut off to the brain then the brain would go to sleep. Lilly decided to test this hypothesis and, with this in mind, created an environment which totally isolated an individual from external stimulation. From here, he studied the origin of consciousness and its relation to the brain.

Peter Suedfeld and Roderick Borrie of the University of British Columbia began experimenting on the therapeutic benefits of flotation tank usage in the late 1970s. They named their technique "Restricted Environmental Stimulation Therapy" (REST).

Initial isolation tank designs involved being entirely submerged in the tank, and users were required to wear complicated head-masks to breathe, along with uncomfortable tight clothing. Many users claimed that the mask and clothing detracted from the isolation experience by creating uncomfortable physical conditions, and that being entirely submerged in water led to the fear of drowning. The tight fit of the mask seal around the face and the retention strips wrapping around the back of the head were uncomfortable in long sessions. The constant hissing of the airvalves and bubbling of exhaust air out of the mask prevented the possibility of silence. The faceplate of the mask was typically solid black for visual isolation, but then the tank user needed help entering and leaving the isolation tank since the mask blinded them. The tight neoprene clothing was extremely uncomfortable in sensitive areas such as the genitalia, and constricted blood flow and mobility in other areas.[5]

In current tanks, a solution of epsom salt is used to increase water density. The user floats with the face above the water, and the ears are submerged when the subject is in a relaxed position. Hearing is therefore greatly reduced, particularly when using ear-plugs as protection against the salt water. When the arms float to the side, skin sensation is greatly reduced because the air and water are the same temperature as the skin, and the feeling of a body boundary fades. The sense of smell is also greatly reduced, especially if the water has not been treated with chlorine. The density of the water prevents rolling over , even if asleep. The growing number of commercial float tanks has brought increased regulation of disinfection. In the US different states have implemented different rules. In Europe, the DIN 19643 bathing water standard requires automated chlorination controlled by REDOX (ORP) measurement. Chlorine, bromine and peroxide disinfection have all been used successfully. There is doubt about ozone safety because of the closed air space. For this reason, H2O2 is cited by many industry professionals as a safer and more desirable sanitation agent.[6]

Generally, users of isolation tanks enter the pool nude. The elastic material of a tight-fitting swimsuit can create uncomfortable compressed stress points on the skin during the session. Due to the high salt content, the water is rarely changed, and all users are expected to shower, wash with soap, and rinse clean prior to entering the tank to avoid getting oils from their skin into the tank. Bathing is again needed after a session to remove excess epsom salt from the skin, and white vinegar is often used to remove excess salt from the ear canal and hair.

Most isolation tanks use a surface skimmer, cartridge filtration, as a means of disinfection, along with ultravioletsterilization and chemicals to keep the water free of microbes and sediment. These machines are usually turned off during a session to keep the isolation space as quiet as possible. A ring heating system can be used around the outer walls of the tank so that warm water rises around the edges of the pool, travels towards the center, and then sinks under the tank user. This very slow water convection flow helps to keep the user centered in the middle of the pool. The small waves caused by breathing also aid in centering the subject.

Cut through a float tank.

Isolation tank construction and plumbing is typically all plastic. In most cases, glass reinforced resins are used. High quality flotation tanks may use acrylic or medical stainless steel which is impervious to the strong salt solution and more importantly the disinfectants. Epsom salt is not corrosive in the way sodium chloride is, but unsealed stone and concrete surfaces outside the tank can be damaged by splashed or dripped salt water as the recrystallizing salt opens up cracks and fissures as it dries. Chlorine used as a disinfectant can attack some surfaces such as marble.

It is useful to have a shower stall in the same room as the tank. Before a session, the tank user can transfer directly from the shower to the tank without drying off, which helps prevent oil from the user's skin from entering the water. Following the session, they can immediately rinse off which minimizes the dripping of corrosive salt through the building.

Having plumbing facilities immediately next to the tank is also helpful when the water must eventually be changed to prevent microbe growth. The plumbing, including the drain pipes, should be constructed of plastic to prevent deterioration from the salt. The salt concentration may need to be diluted when discarded, to prevent damage to small private wastewater plumbing systems.

A therapeutic session in a flotation tank typically lasts between an hour to an hour and a half. For the first forty minutes, it is reportedly possible to experience itching in various parts of the body (a phenomenon also reported to be common during the early stages of meditation). The last twenty minutes often end with a transition from beta or alpha brainwaves to theta, which typically occurs briefly before sleep and again at waking. In a float tank, the theta state can last indefinitely without the subject losing consciousness. Many use the extended theta state as a tool for enhanced creativity and problem solving or for super learning. The more often the tank is used the longer the theta period becomes.[7]

Spas sometimes provide commercial float tanks for use in relaxation. Flotation therapy has been academically studied in the USA and in Sweden with published results showing reduction of both pain and stress.[8] The relaxed state also involves lowered blood pressure and maximum blood flow.

Floating can be passive or active, depending on the purpose. For relaxation, one simply floats and 'clears the mind.' Active floating has many different techniques. One may perform meditation, mantras, self-hypnosis, utilize educational programs, etc. The idea of active floating is that, when the body is relaxed, the mind becomes highly suggestible and any action taken during these states will enter the information into the sub-conscious. Flotation therapy may be used to complement other body work and healing methods.

Flotation therapy is therapy that is undertaken by floating in a warm salt water in a float tank.[9]

Flotation therapy developed from the research work of John Lilly although he was not primarily interested in therapy, rather in the effect of sensory deprivation on the human brain and mind.

People using early float tanks discovered that they enjoyed the experience and that the relaxed state was also a healing state for many conditions including stress, anxiety, pain, swelling, insomnia and jet lag.

As a result float tanks were produced for commercial uses and commercial float centers offering flotation therapy opened in several countries during the period from 1980 to the present day when there are hundreds of flotation centers in dozens of countries. In almost all cases these float centers offer wellness treatments and in particular the release of stress. The San Francisco Bay Area has seen recent growth in such centers.[10]

Research into flotation therapy (as opposed to just the effect of isolation) began in the USA at Ohio State University where floating was shown to improve creativity in Jazz musicians, accuracy in rifle shooting, focus before academic examinations and stress relief, among others.[11]

Research in Sweden has demonstrated the therapeutic effect on stress and pain.[12]

The technique takes advantage of an innate, natural inclination to relax when floating at a comfortable temperature. The temperature is that which allows natural heat generation to escape without the need for muscle action to raise body temperature in homeostasis. The floating posture, usually the supine position (although the prone position with chin supported on elbows is recommended for pregnant women), allows all the postural muscles to relax. The water pressure on the immersed skin is lower than the blood pressure and thus blood flow continues in skin capillaries. This is in contrast to normal bed rest where local contact pressure inhibits blood flow requiring regular adjustment of posture. When people cannot adjust their posture in bed, e.g. in some illnesses, bed sores can result. When floating there is no tendency to adjust posture and a person can float immobile for many hours.

The natural tendency of the body in the floating posture at the correct temperature is to dilate the blood vessels, reducing the blood pressure and maximizing blood flow. The brain activity normally associated with postural muscles is reduced to a minimum. In this state, which we can call the floating state, natural endorphins are released reducing pain.[12][13]Lactic acid removal is accelerated. Flow in the lymphatic system is increased.

Perceived stress can be correlated with increased levels of cortisol and in flotation therapy there is a natural tendency for cortisol to be reduced.[14] For this reason, flotation therapy is one of the few noninvasive techniques available to manage stress when it is a factor in reducing a person's ability to cope with normal life. Flotation therapy is a fast technique in this respect. The Swedish research was based on 40 minute float sessions. This compares well with other management techniques such as long vacations.

There are some similarities with the age old long hot bath. However, the main differences are that in floatation all sensory impressions are absent, temperature is maintained at the correct level and the bath is large enough to float without touching the sides of the float unit. These factors allow the individual to achieve much deeper level of relaxation, and therapeutic benefit, than would otherwise be possible.

Most float tanks use Epsom salt, magnesium sulfate, in high concentration so that the relative density of the solution is about 1.25. (Lilly recommended 1.3 but this requires operating very close to saturation with the risk of recrystallization). The density assists floating particularly making the head buoyant so that the nose and mouth are well out of the water for breathing.

It has recently been discovered that there is a secondary effect which is important to flotation therapy. Magnesium is absorbed through the skin due to natural molecular diffusion. This tends to correct magnesium deficiency.[15] Magnesium is absorbed from the diet but in many areas of the world, over-cropping without adequate replacement of magnesium makes the normal diet low in magnesium.

The body naturally optimizes the levels of magnesium, so there is no overload effect from floating in the salts for extended periods.[citation needed]

It is noted that there is no "flotation therapist", although there is a need to instruct the floater and need to maintain the equipment in a safe condition. However, flotation therapy is compatible with other therapies as a preparation or conjunct activity. Examples include massage, talk therapy, and hypnosis.

Research undertaken at the Human Performance Laboratory at Karlstad University Sven-Åke Bood[16] concludes that regular flotation tank sessions can provide significant relief for chronic stress-related ailments. Studies involving 140 people with long-term conditions such as anxiety, stress, depression and fibromyalgia found that more than three quarters experienced noticeable improvements.

Dr. Bood commented: "Through relaxing in floating tanks, people with long-term fibromyalgia, for instance, or depression and anxiety felt substantially better after only 12 treatments". Research targeted the effectiveness of floatation treatment with regard to stress related pain and anxiety over the period of seven weeks. 23 percent of the participants became entirely free of pain and 56 percent experienced clear improvement.

Broken down to various symptoms, the results were as follows: 23 percent slept better opposed to __% controls, 31 percent experienced reduced stress opposed to __% controls, 27 percent felt less agony opposed to __% controls, and 24 percent became less depressed or got rid of their depression altogether opposed to __% controls. The research also confirms the findings of an earlier thesis that flotation, after only twelve sessions, substantially improves sleep patterns leaving users more optimistic and with reduced nervousness, tension and pain. Relaxing in a weightless state in the silent warmth of a flotation tank activates the body's own system for recuperation and healing, said Sven-Åke Bood. What researchers find particularly gratifying is that the positive effects were still in evidence 4 months after the floating treatment ended.

In a number of recent videos on YouTube and his own podcast, American stand-up comedian and television celebrity Joe Rogan describes his personal experiences with isolation tanks and shares his insights into using them for various purposes, such as exploring the nature of consciousness and improving health and well being.[17]

The British glass artist Jeremy Langford is a devoted user of the tank. In few of his interviews he mentioned the flotation tank as a tool for enhancing creativity.